The present invention generally relates to touch sensors and, more particularly, to a method for determining a touch position on the touch sensor using a touch slider.
Touch sensors are useful in Human-Machine Interface (HMI) applications. Touch sensors can be used in toys, white goods, etc. for adjusting specific user parameters, such as brightness and volume or for scrolling displayed menus.
A touch sensor includes electrodes that when touched, detect a change in resistance or capacitance thereof and generate a trigger signal. The trigger signal is input to a controller or processor to determine the position of the touch on the touch sensor.
FIG. 1 is a schematic diagram of a touch sensor 10. The sensor includes an electrode 102 and an optional electrode 104. The electrodes 102 and 104 are triangular in shape, mutually complementary, and arranged to form a rectangle. The electrodes 102 and 104 are coupled to a controller 12. The controller 12 includes input terminals Chn0 and Chn1 corresponding to and respectively coupled with the electrodes 102 and 104. Touch positions like P0 and P1 are shown at the bottom of the figure to avoid overlapping the labels of the electrodes, although in practice touch positions could be exactly on the electrodes. When the electrodes 102 and 104 are touched, such as by a user's fingers, there is a change in the resistances or capacitances of the electrodes. Table 1 shown in FIG. 6A is an exemplary correspondence table that maps the values of the received signals on the input terminals Chn0 and Chn1 with the touch positions.
In response to the received signals, the touch position can be determined by looking up the value of the received signals in the table. However, the values of the received signals suffer greatly from noise. The signals provided by the electrodes tend to be coupled, especially in white goods applications, with noise from power supplies, which makes it difficult to accurately determine the position of the touch.
FIG. 2 is a schematic diagram of another touch sensor 20. The touch sensor 20 includes a plurality of electrodes E0-E5, and a controller 22 coupled with the electrodes E0-E5 for receiving trigger signals therefrom. The controller 22 includes input terminals Chn0-Chn5 corresponding to and coupled with respective ones of the electrodes E0-E5. As shown in FIG. 2, when the electrode E0 is touched, for example in the position P0, a parameter of the electrode E0, for example capacitance when the electrode is a capacitive sensing element or resistance when the electrode is a resistive sensing element, will change. The signal that the electrode E0 provides to the corresponding input terminal Chn0 of the controller 22 changes accordingly. The controller 22 determines the touch position P0 using the signal received from the electrode E0. If more than one of the electrodes, for example electrodes E2 and E3 are simultaneously touched at the position P1, both electrodes E2 and E3 responsively show parameter changes and in turn provide the controller 22 with changed signals at input terminals Chn2 and Chn3. The position P1 is determined by the controller 22 through the received signal composition.
Table 2 shown in FIG. 6B shows an exemplary correspondence table that maps the values of the received signals on the input terminals Chn0-Chn5 with the touch positions:
In Table 2, the values of the received signals on the input terminals Chn0-Chn5 are digitized to accommodate for noise, and each electrode E0-E5 is configured to a corresponding input terminal Chn0-Chn5 of the controller 22 with a given granularity related to human finger sizes. For example, a larger sensor with more electrodes will require the controller to have more input terminals, which may adversely affect the size of the controller.